by David Wallace
Updated July 20, 2026
Polycythemia is defined as having an abnormally high number of red blood cells in the blood—derived from the Latin “poly” (many), “cyte” (cell), and “hemo” (blood). This general term encompasses various conditions leading to this hematological abnormality.
Polycythemia Vera (PV) fits under this umbrella but has its own classification. This article delves into the distinctions between these related but unique hematological conditions, covering definitions, causes, symptoms, diagnostic approaches, and management strategies.
Definitions and Classifications
Polycythemia
Polycythemia can be classified into two main categories based on underlying causes:
- Primary Polycythemia: Resulting from intrinsic bone marrow disorders causing excessive red blood cell production.
- Secondary Polycythemia: Arising from external factors or conditions that increase erythropoietin production and stimulate red blood cell production.
Polycythemia Vera (PV)
PV is a specific type of primary polycythemia classified as an MPN, a rare blood cancer. It falls under the myeloproliferative neoplasm (MPN) category and is characterized by:
- Chronic, progressive nature.
- Excessive production of red blood cells, white blood cells, and platelets.
- An acquired genetic mutation, often in the JAK2 gene (approximately 95%), that disrupts normal blood cell production.
Causes and Blood Cell Production
Causes of Polycythemia Vera
PV results from an acquired mutation in the JAK2 gene, which regulates blood cell production. This mutation causes unregulated blood cell proliferation. While the trigger for this mutation remains unclear, environmental factors like exposure to radiation or certain chemicals have been hypothesized.
Causes of Secondary Polycythemia
Secondary polycythemia results from increased erythropoietin levels due to:
- Hypoxia (e.g., high altitude, sleep apnea, chronic lung disease).
- Tumors producing erythropoietin.
- Smoking or chronic carbon monoxide exposure.
- Kidney diseases affecting erythropoietin regulation.
Unlike PV, secondary polycythemia generally affects only red blood cell production, sparing white blood cells and platelets.
Diagnosis and Diagnostic Criteria
Accurate diagnosis requires distinguishing between PV and secondary polycythemia. A key diagnostic marker is serum erythropoietin (EPO) levels:
- Low EPO levels: Indicative of PV, as uncontrolled red blood cell production suppresses erythropoietin.
- Normal or high EPO levels: Common in secondary polycythemia, reflecting the body’s response to hypoxia or other stimuli.
Diagnosing Polycythemia Vera
- Complete Blood Count (CBC): Elevated red blood cells, hemoglobin, and hematocrit.
- Serum EPO levels: Typically low in PV, a distinguishing feature as supported by recent research.
- Genetic Testing: Detection of JAK2 mutations, found in 95% of PV cases.
- Bone Marrow Biopsy: Reveals abnormal blood cell production patterns.
Diagnosing Secondary Polycythemia
- EPO Levels: Elevated in response to hypoxia or tumors.
- Arterial Blood Gas Analysis: To assess oxygen levels.
- Imaging: To detect tumors or evaluate lung and heart function.
- Sleep Studies: To rule out sleep apnea.
Treatment Approaches
Treatment of Polycythemia Vera
- Phlebotomy: Regular blood removal reduces red blood cell mass, maintaining normal hematocrit levels.
- Medications:
- Besremi (Ropeginterferon alfa-2b): A long-acting interferon approved specifically for PV.
- Pegasys (Peginterferon alfa-2a): Regulates bone marrow activity and reduces blood counts.
- Hydroxyurea: Suppresses bone marrow activity but has potential long-term side effects.
- Ruxolitinib: A JAK inhibitor for refractory cases.
- Low-dose Aspirin: Reduces the risk of blood clots.
- Lifestyle Modifications: Smoking cessation, hydration, and avoiding extreme temperatures.
Treatment of Secondary Polycythemia
- Addressing the underlying cause, such as managing sleep apnea or treating tumors.
- Temporary phlebotomy to relieve symptoms in severe cases.
What This Means for You
If you have been told your red blood cell count is high, the important next question is why. A high hematocrit alone does not mean you have polycythemia vera. Dehydration, sleep apnea, smoking, high-altitude living, and testosterone therapy all raise red cell counts without any blood cancer involved.
The tests that answer the question are straightforward: a serum EPO level and JAK2 mutation testing. If both point toward PV, a bone marrow biopsy typically confirms it. If you have been given a PV diagnosis without those tests, it is reasonable to ask for them.
Resources to Help You Take the Next Step
- MPN Specialist Directory: find a verified MPN specialist by state
- What Is Polycythemia Vera?: a full overview of the disease
- Questions to Ask Your Doctor: what to bring to your next appointment
- PV for Newbies: a starting guide for the newly diagnosed
- MPN Cancer Dictionary: plain-language definitions of terms you will hear
Frequently Asked Questions
Is polycythemia the same as polycythemia vera?
No. Polycythemia is a general term for having too many red blood cells, and it has many possible causes. Polycythemia vera is one specific cause: a chronic blood cancer driven by an acquired JAK2 mutation. All polycythemia vera is polycythemia, but most polycythemia is not polycythemia vera.
What is the difference between polycythemia and erythrocytosis?
The terms are often used interchangeably. Erythrocytosis refers specifically to an increase in red blood cells, while polycythemia is sometimes used more broadly, including cases where white blood cells and platelets are also elevated, as often happens in polycythemia vera.
Is polycythemia the opposite of anemia?
In a general sense, yes. Anemia means too few red blood cells or too little hemoglobin, while polycythemia means too many. Both conditions affect how efficiently oxygen is carried through the body, but they have entirely different causes and treatments.
Can secondary polycythemia turn into polycythemia vera?
No. Secondary polycythemia does not develop into polycythemia vera. They have different underlying mechanisms: PV is caused by a mutation in bone marrow stem cells, while secondary polycythemia is the body responding to an external trigger such as low oxygen. A patient initially diagnosed with secondary polycythemia may later be found to have PV, but that reflects a corrected diagnosis rather than one condition becoming the other.
What EPO level indicates polycythemia vera?
A low serum erythropoietin level is a hallmark of polycythemia vera, because the overproduction of red blood cells suppresses the body’s EPO signal. Normal or elevated EPO points instead toward secondary polycythemia. EPO testing is used alongside JAK2 mutation testing and, in most cases, a bone marrow biopsy rather than on its own.
Is secondary polycythemia dangerous?
Secondary polycythemia raises blood viscosity, which can increase clotting risk, so it should be evaluated and monitored. It is generally less serious than polycythemia vera because it is not a cancer and often improves when the underlying cause is treated. The right approach depends on the cause and on how elevated the counts are, which is a conversation to have with your doctor.
Medical Disclaimer
This article is for educational and patient advocacy purposes. It is not medical advice and is not a substitute for consultation with a qualified hematologist or MPN specialist. Diagnosis and treatment decisions should always be made in partnership with your healthcare team.
About the Author
David Wallace is a polycythemia vera patient advocate, writer, and the founder of PV Reporter and MPN Cancer Connection. Since launching PV Reporter in 2013, he has built one of the most comprehensive patient resource hubs for myeloproliferative neoplasms, including a doctor-vetted MPN specialist locator and a free clinical trial finder. David attends the American Society of Hematology annual meeting with press credentials and writes about emerging MPN research from the patient perspective.
Diagnosed with PV in May 2009 and now in complete molecular remission, his advocacy work has supported MPN patients and caregivers around the world.
Read David’s full bio at PV Reporter
References
- Tefferi, A., & Barbui, T. (2017). Polycythemia vera and essential thrombocythemia: 2017 update on diagnosis, risk-stratification, and management. American Journal of Hematology, 92(1), 94-108.
- Khorshid, A., González, D., & Zhang, J.-Z. (2024). Evaluation of hemoglobin and serum erythropoietin levels in patients with polycythemia vera and secondary polycythemia. Research Square.
- McMullin, M. F. (2016). Diagnosis and management of congenital and idiopathic erythrocytosis. Therapeutic Advances in Hematology, 7(3), 172-180.
- Spivak, J. L. (2019). Myeloproliferative Neoplasms. New England Journal of Medicine, 380(22), 2168-2181.
